The present invention relates to an image pickup apparatus and its driving method.
Firstly, description is given on the first related art. Conventionally, there have been proposed various systems for driving an image pickup apparatus. For example, there is known a method of driving an image pickup apparatus in a horizontal direction and vertical direction by using a scanning circuit utilizing a shift register. An example of constituting an image pickup apparatus utilizing such a driving system is shown in FIG. 30. The image pickup apparatus of such constitution comprises a pixel 1101 comprising the photoelectric conversion elements arranged in a two-dimensional array form, a horizontal selection line 1102 provided in coordination with the pixels 1101 arranged in the row direction of the two-dimensional arrays, a horizontal scanning circuit 1105 for selection of row, a horizontal selection switch 1103 provided in coordination with the horizontal selection line 1102, an output signal line 1104 connected commonly with the horizontal selection switch 1103, a horizontal selection line 1106 provided in coordination with the pixel 1101 arranged in the line direction of the two-dimensional arrays, and a vertical scanning circuit 1107 for selection of line, and is constituted to be driven by the sequential application of the driving clock to the horizontal scanning circuit 1105 and the vertical scanning circuit 1107.
With respect to the constitutions of the horizontal scanning circuit 1105 and the vertical scanning circuit 1107, there is known, for example, one made by utilizing a clock type CMOS shift register by connecting the clock type inverters in series. An example of the constitution of the shift register is shown in FIG. 31. In FIG. 31, the part 1108 is a first clock type inverter, and 1109 is a second clock inverter. The first and second clock type inverters 1108 and 1109 are connected in series to constitute a shift register unit 1110, and a large number of shift register units 1110 are connected in series to constitute a shift register, i.e. a scanning circuit. This can be represented in a schematic symbol as in FIG. 32.
FIGS. 33A-33H are timing charts for illustrating the operations. The clock is in two phases of .PHI.1 and .PHI.2. By application of the start pulse .PHI.ST to the input of the shift register unit 1110, .PHI.SR1, .PHI.SR2, .PHI.SR3, . . . are sequentially outputted from the output terminals of the shift register units 1110, in synchronization with the start-up of the clock .PHI.1. In FIGS. 31, 33C, and 33D, /.PHI.1 and /.PHI.2 show the inverted clocks of the .PHI.1 and .PHI.2.
Next, the timing charts to show a driving examples in the case of using the shift register of the above constitution for the vertical scanning circuit 1107 are shown in FIGS. 34A-34L. In FIGS. 34A-34L, .PHI.V1, .PHI.V2, and .PHI.VST correspond to .PHI.1, .PHI.2, and .PHI.ST in the shift register unit 1110 stated above, and /.PHI.V1, /.PHI.V2 show the inverted clocks of .PHI.V1, .PHI.V2. Further, .PHI.SR1, .PHI.SR2, .PHI.SR3, . . . are used as the vertical selection pulses for selecting the line directional lines of the two-dimensional array. In FIGS. 34A-34L, the pulses for driving the vertical scanning circuit 1107 are the two phases of .PHI.V1 and .PHI.V2., and, by the application of the start pulse .PHI.VST, the vertical selection pulses .PHI.SR1, .PHI.SR2, .PHI.SR3, . . . are sequentially outputted in synchronization with the start-up of the clock .PHI.V1. In FIGS. 34A-34L, in case of the high levels of the vertical selection pulses .PHI.SR1, .PHI.SR2, .PHI.SR3, . . . mean that the pixels of the corresponding lines are selected. Also, the period from the falling of the .PHI.V1 to the starting-up of the .PHI.V1 is the horizontal blanking period (HBL). As shown in FIG. 34A-34L, by applying .PHI.V1 and .PHI.V2 once each, the vertical selection pulses .PHI.SR1, .PHI.SR2, .PHI.SR3, . . . are sequentially transferred to drive the pixels.
Hereinafter, the second related art will be described. In an image pickup apparatus for shooting the object in high precision, as the number of pixels of the image pickup device increases, the driving frequency of the image pickup device is required to be increased. For example, the driving frequency of the image pickup device used in HDTV (High Definition Television) reaches 74.25 MHz. In practice, it is difficult to make an image pickup device of such high frequency (high speed), and the manufacturing cost of a circuit for processing data at a high speed is high. Accordingly, conventionally, in an image pickup apparatus for recording high precision still images, the field rate is lowered, and the image data of one field or one frame portion is read out at relatively low speed and recorded.
FIG. 35 is a block diagram showing an example of constitution of an image pickup apparatus relating to the second related art. In this constitution example, an object is focused by the lens 1201 on the CCD (Charged Coupled Device) image pickup device 1202 and photoelectric conversion is performed. This CCD image pickup device 1202 is driven by the timing pulse generated from the driving part 1203. The image data read out from the CCD image pickup device 1202 is provided with signal processing such as a gain adjustment in the signal processor 1204, after which it is converted into digital data by the non-illustrated analog/digital converter (hereinafter to be referred to as A/D converter) and outputted.
The recorder 1205 is to record the digital data as still images, and is constituted by various recording media such as the semiconductor memory. The display signal processor 1206 is to output the above digital data by converting into the standard television signal. It is constituted by a synchronous signal addition circuit, digital/analog converter (hereinafter to be referred to as D/A converter), and the like. The system controller 1207 is to make sequential control of the whole image pickup apparatus, and is constituted by microcomputer and the like. The trigger switch 1208 is a shutter button to be operated when the operator desires to take in a still image.
Next, the operation of the image pickup apparatus constituted as above is explained. When the operator depresses the trigger switch 1208, the system controller 1207 detects the said depression. At this time, the system controller 1207 sends the exposure starting and exposure ending timing signals to the driver 1203, and sends the recording start timing signal to the recorder 1205. The driver 1203 generates, on receipt of the exposure starting and ending timing signals, a timing pulse necessary for exposure and reading out in the CCD image pickup device 1202. The image signal read out by the CCD image pickup device 1202 on the basis of this timing is provided with the predetermined processing in the signal processor 1204 and then memorized in the recorder 1205.
At this time, the driving frequency of the CCD image pickup device 1202 is about 10-20 MHz. Assuming that this CCD image pickup device 1202 is constituted by the high pixel sensor of horizontal 2048.times.vertical 2048 pixels and its driving frequency is 10 MHz, it means that the time of 0.4 second is required to read out the image data of one picture (1 frame) from the said CCD image pickup device 1202. Namely, the frame rate becomes about 2.5 frames/second.
Prior to this recording operation, for adjusting the focal length or image angle to the object, the operator monitors the object with the non-illustrated display apparatus connected to the output side of the display signal processor 1206. During this monitoring, the driver 1203 carries out continuously the exposure and reading out in the CCD image pickup device 1202. The read out image data are provided with the predetermined signal processing with the signal processor 1204 and inputted to the display signal processor 1206. And, the display signal processor 1206 thins out the inputted image data, and stores the image data after thinning out in the own memory for display at a predetermined rate. The recorder 1205 reads out the image data stored in the memory for display in order to convert it into a standard television signal, and outputs it after converting into analog signal by adding a synchronous signal thereto.
Hereinafter, the third related art is explained. The color solid image pickup device in the image pickup apparatus is utilized in various image apparatuses including the video camera for recording moving pictures and electronic still camera for taking still images, and the like.
In recent years, due to the progress of the semiconductor techniques, the color solid image take-up devices with several million pixels have been developed and practically used in the electronic still cameras which require high resolution. However, even such high resolution cameras with the resolution in excess of several million pixels may be required to have a capacity to record moving pictures (not necessarily having high resolution). However, such high resolution cameras are provided for still picture, and they are not able to take the moving pictures. It is because of the fact that, in proportion to the increase in the number of the pixels the time required for the color solid image pickup device to reading out the signal increases.
In order to settle this problem, hitherto there has been proposed a technique to make reading out with substantially reduced pixels by such means as to set the reading out frequency of the color solid image pickup device higher in the case of taking moving pictures than in the case of taking still pictures or to thin out the signals of the color solid image pickup device.
The problematic points of the first, second, and third related techniques as described above are explained below.
In the image pickup apparatus relating to the first related technique above, in the conventional driving method using a shift register for sequentially transmitting the selected pulses, the following points occur. Namely, in the image pickup apparatus of the constitution as shown in FIG. 30, each unit of the vertical scanning circuit 1107 corresponds one by one to the vertical selection line group 1106 provided in coordination with the pixel 1101 which is a photoelectric conversion element arranged in the line direction. Therefore, when the image pickup apparatus having the constitution as shown in FIG. 30 is driven in the driving method as described above, only the non-interlace driving can be made, so that the camera system using this image pickup apparatus is usable solely for the non-interlace application. On the other hand, in order to realize the interlace scanning, there is a scanning system as disclosed in Japanese Patent Publication (Unexamined) No. 5-300433/1993 applied by the applicant of the present invention. However, such a system involves a problem of increased number of clock groups to be applied to the scanning circuit.
In the image pickup apparatus utilizing the second related technique stated above, the frame rate of the image data inputted to the display signal processor 1206 is about 2.5 frames/second. Here, even assuming the frame rate of the standard television signal outputted is 30 frames/second which is based on the NTSC (National Television System Committee) system, it follows that the same image is outputted from the display signal processor 1206 for the duration of 0.4 second until the image data of the memory for display is re-written.
Accordingly, in the image pickup apparatus made in respect to the second related technique as stated above, in monitoring an object with a display unit for the purpose of focus adjustment or image angle setting, because of the slow frame rate for the re-writing of the image data, delay of response is caused to give a problem of poor convenience of use.
Also, according to the technique to change over the reading out frequency of the signal of the image pickup device of the image pickup apparatus to read out in a high frequency relating to the third related technique, when the required resolution becomes high and the driving frequency becomes high, various problems are involved in the point of the practical use with respect to the response characteristic of the circuit and power consumption.
For example, the driving frequency of the color solid image pickup device having 2-million pixels (2000.times.1000) for high vision is 74 MHz, and the driving frequency of the color solid image pickup device having 4-million pixels (2000.times.2000) becomes extremely high frequency of as high as 148 MHz.
As the color difference sequential system or Bayer system which is generally adopted in the color filter layout adopts repetition of pixel arrangements in the primary unit of 8 pixels of 2 (horizontal).times.4 (vertical), for example, in case of the thinning of the pixels to 1/2.sup.n (n: natural number) in horizontal and vertical numbers, only the signal of the specified color is read out, and no color image pickup can be made.